The present invention relates generally to a seat belt buckle, and more particularly to a seat belt buckle suitable for use in motor vehicles.
A seat belt buckle provides a readily releasable mechanism for securing the ends of a seat belt and/or shoulder belt in a predetermined position to restrain an occupant of a vehicle during a collision.
One form of seat belt buckle in use particularly in Europe has a side operated push button rather than a top push button and employs a lock pin or latch bar which is positioned to block release of a latching dog from locking engagement with a tongue plate until the push button is operated. Usually, the lock pin or bar is mounted to slide in slots in the frame and is shifted by movement of the push button from a blocking position over the latch dog to release position in which the latch dog is free to pivot from latching engagement with the tongue plate. In such buckles, the push button is typically biased toward an outer position and is pushed inward to open the latch mechanism.
Various government and industry standards impose requirements on seat belt buckles which are to be used in motor vehicles. To comply with such standards, a seat belt buckle should be able to withstand relatively high tensile forces without deforming substantially and without releasing the tongue plate when the latching means is in its latched position. In addition, the buckle should be releasable upon the application of a reasonable amount of force to the push button even if a person is hanging upside down from the seat belt. That is, in the event of an accident where a vehicle has overturned and the weight of the driver is supported by the belt, the tension on the buckle should not make it overly difficult to open. Also, the latching means should not release accidentally due to impact or vibration, but should be releasable only by actuation of the push button.
It is further desirable that the seat belt buckle provide a clear indication to the user as to whether it is latched when the tongue plate is inserted into the buckle frame so as to avoid false latching conditions. To this end, some seat belt buckles employ ejectors which urge the tongue plate forwardly of the buckle frame to eject it therefrom if the tongue plate is within the buckle but not latched in place.
In the past, seat belt buckles of the type having a spring-biased push button in combination with an ejector have generally employed relatively complicated mechanisms which include at least two separate springs, and have commonly used coil springs loaded in compression. Use of coil springs loaded in compression may be more expensive than use of coil springs loaded in tension for analogous functions, because a coil spring loaded in compression may buckle when loaded instead of compressing along a desired line or curve, and the design constraints on compression springs may need to be more narrowly defined to prevent such buckling.
Side release buckles of the foregoing kind are produced in large numbers for use as original equipment on automobiles. Hence, savings in parts, raw material costs, and assembly of the buckles are important and may make the difference between a buckle being commercially successful or unsuccessful. In addition to costs, there is today a preference for small, lightweight buckles. Conflicting with the preference for small, lightweight buckles is the competing demand by automotive companies that buckles be capable of handling heavier loads than heretofore, e.g., 5000 lb. tensile loads.